1. Field of the Invention
The present invention relates to a method of making an insulated-gate field effect transistor, and more specifically relates to improvements in forming electrical contacts to source and drain regions of the transistor.
2. Description of the Related Art
In the very, large scale integrated circuit device, electrical contacts to the source and drain regions of the insulated-gate field effect transistor have been formed according to the following conventional manufacturing process as shown in FIGS. 1A-1F.
First, an oxide film 202 for element isolation is formed on a silicon substrate 201 for isolating individual element areas from each other on the substrate 201, and thereafter a gate-insulating oxide film 210 is formed on the area surrounded by the isolating oxide film 202. Then, polysilicon gates 203, 203' are formed by means of the photolithography technology (FIG. 1A). Thereafter, oxide films 204, 204' are formed to cover the respective polysilicon gates 203, 203' including the sides thereof (FIG. 1B). Then, diffusion regions 205 and 205' are formed to constitute source and drain regions (FIG. 1C). An insulating inter-layer 206 is deposited on the substrate 201 (FIG. 1D), and thereafter contact holes are opened by means of the photolithography technology (FIG. 1E). Lastly, aluminum wirings 207, 207' and 207" are provided through the contact holes to form electrical contacts to the source and drain regions 205 and 205' (FIG. 1F).
In the above-mentioned conventional method of manufacturing the insulated-gate field effect transistor, the distances between these contact holes and the polysilicon gate is restricted to a certain limit due to an alignment margin of the photolithography technology and process margin in etching the insulating inter-layer to open the contact holes. For this reason, the miniaturization of insulated-gate field effect transistor cannot be effectively achieved. In addition, during the process of providing the aluminum wirings, the aluminum wirings must clear steeply etched step portions of the contact hole, hence there is a drawback that the miniaturization of the insulted-gate field effect transistor would cause breaking of the aluminum wirings.